Add awakened_from_remote() to bypass remote_ready_queue

[Akatsukis]

Depends on #2

[Copilot]

Pull request overview

This PR adds an optional awakened_from_remote() hook on algorithm so that schedulers with thread-safe ready-queues can bypass the per-thread remote_ready_queue_ when schedule_from_remote() is invoked. It also (apparently inheriting from a dependent PR) removes the sleep-queue mechanism and all timed-wait/sleep public API along with associated tests and examples, and replaces algorithm::suspend_until with a parameterless suspend().

Changes:

• Add algorithm::awakened_from_remote() virtual hook (default returns false) and integrate fast-path in scheduler::schedule_from_remote, plus a new worker_splk_ to serialize attach/detach of worker contexts across threads.
• Remove the sleep queue and all wait_until/wait_for/sleep_for/sleep_until API surface from scheduler, context, condition_variable[_any], future/shared_future, buffered_channel, operations, and wait_queue.
• Delete the corresponding _post/_dispatch test files and the priority/wait_stuff examples, with matching removals in test/Jamfile.v2 and examples/Jamfile.v2.

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
include/boost/fiber/algo/algorithm.hpp	Replace suspend_until with suspend; add awakened_from_remote default hook.
include/boost/fiber/algo/round_robin.hpp	Override suspend() instead of suspend_until.
src/algo/round_robin.cpp	Implementation now waits unconditionally on the cv.
include/boost/fiber/scheduler.hpp	Remove sleep-queue type/state and wait_until; add worker_splk_ and AWAKENED_FROM_REMOTE guards.
src/scheduler.cpp	Remove sleep2ready_/wait_until; integrate awakened_from_remote fast path; lock worker_splk_ in attach/detach/terminate/dispatch.
include/boost/fiber/context.hpp	Drop sleep_hook, sleep_waker_, tp_, sleep_*/wait_until members.
src/context.cpp	Remove wait_until and sleep_* definitions/asserts.
include/boost/fiber/waker.hpp, src/waker.cpp	Remove suspend_and_wait_until.
include/boost/fiber/condition_variable.hpp	Remove wait_for/wait_until overloads on cv and cv_any.
include/boost/fiber/buffered_channel.hpp	Remove push_wait_for/until and pop_wait_for/until.
include/boost/fiber/future/future.hpp, .../shared_state.hpp	Remove wait_for/wait_until.
include/boost/fiber/operations.hpp	Remove sleep_for/sleep_until.
test/Jamfile.v2	Drop test entries for the removed _post/_dispatch test files.
test/test_fiber_{post,dispatch}.cpp, test/test_mutex_, test/test_condition_variable*, test/test_future, test/test_shared_future_, test/test_buffered_channel_*	Deleted.
examples/Jamfile.v2, examples/priority.cpp	Remove priority and wait_stuff examples.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (3)

include/boost/fiber/scheduler.hpp:86

• worker_splk_ is currently always part of scheduler's object layout even when BOOST_FIBERS_AWAKENED_FROM_REMOTE is not defined, despite the comment indicating it's only needed for that feature. This adds size/ABI surface and can trigger -Wunused-private-field warnings in builds that don't enable the macro. Consider making the member conditional like remote_ready_splk_ so default builds keep the previous layout.

    // When BOOST_FIBERS_AWAKENED_FROM_REMOTE is defined, worker_splk_
    // serializes attach/detach_worker_context so a remote thread calling
    // ctx->detach() inside awakened_from_remote() doesn't race the owning
    // thread's attach of another fiber.
    detail::spinlock                                            worker_splk_{};

src/scheduler.cpp:171

• The awakened_from_remote fast-path can be invoked for main-context wakeups too (schedule_from_remote explicitly allows signaling main-context). If an algorithm implements awakened_from_remote by detaching/migrating contexts, calling ctx->detach() on a main-context will hit detach_worker_context() and assert because main-contexts are not in worker_queue_. Consider restricting the fast-path to worker_context instances so main-context wakeups continue to use the existing remote_ready_queue_ path.

    if ( ! ctx->is_context( type::pinned_context) ) {

src/scheduler.cpp:170

• New behavior is introduced under BOOST_FIBERS_AWAKENED_FROM_REMOTE (bypassing remote_ready_queue_ via algorithm::awakened_from_remote), but there are no existing tests referencing awakened_from_remote. Given the repo has multithreaded scheduling tests, it would be good to add a focused test that enables the macro and verifies (1) awakened_from_remote is called for remote wakeups, and (2) the fallback remote_ready_queue_ path is still used for pinned contexts / when awakened_from_remote returns false.

#if defined(BOOST_FIBERS_AWAKENED_FROM_REMOTE)
    // Let the algorithm handle cross-thread scheduling directly if it
    // supports a thread-safe ready-queue (e.g. a shared priority queue).
    // The subsequent ctx->detach() inside awakened_from_remote() is
    // serialized against the owning thread's attach by worker_splk_.